Raiden is a popular and influential series of vertical Shoot 'em Up created by Japanese developer Seibu Kaihatsu, and later handled by MOSS. It is quite notable for popularising (though not necessarily creating) many concepts and conventions still used by vertical shmups today. Spawned the Raiden Fighters series.The plot of the series is completely nonexistent and inconsequential, much like most shoot'em ups. The gist is that a race of aliens called the "Cranassian Empire" is invading Earth, and it's up to the Raiden supersonic jet to stop them.The series is composed of the following games:
Raiden (later ported to the SNES and Genesis as Raiden Trad)
Raiden DX (an extension of Raiden II with a more elaborate scoring system and several different modes)
Boring but Practical: The red Spread Shot, mostly because if (if) you can nose up close enough to an enemy to make all of the spray hit it, it will suffer more damage more quickly than even with the full-power blue laser. It is not uncommon to get a mid-sized enemy destroyed this way before it can even start shooting. At further range, the spread is wide enough that anything in front of you will continously be pelted with damage, the only drawback being that you have to mash on the fire button, unless you use autofire or play Raiden III or IV, which officially have autofire for this weapon. To summarize, red is your standard-purpose, blue is for concentrated power when point-blank is not an option, and purple/green is for blue purposes that also need you to hit things behind that strong opponent.
Bullet Hell: Later games have denser bullet patterns, although the focus remains on fast aimed shots.
Damn You, Muscle Memory: The 360 port of Raiden IV offers a 360 mode that has all 5 stages plus two extra stages. At first glance that's the only difference, but if you're familiar with Arcade mode, you'll notice that 360 mode changes around the placements of many enemies, which can throw you off.
In II, player 1 starts with standard bombs, while player 2 starts with cluster bombs.
An odd example induced by porting tweaks: In the Japanese version of the PS1 port found in Raiden Project player 1 does not have checkpoints and continues through the stage if they are killed and respawn. But player 2 gets checkpoints, going back to the last one upon death.
In DX, the player 1 ship moves faster vertically, while the player 2 ship moves faster horiztonally.
Double Play: The home ports of both III and IV have a mode where you can control both ships on the same controller.
Grievous Harm with a Body: In II and DX, destroyed airborne enemies have a pretty good chance of crashing into the ground instead of just exploding in mid-air. If their landing point happens to be on top of a ground enemy, that poor enemy is going to be hurting (if not destroyed outright). Like with the things noted in Serial Numbers Filed Off, this is another element from Toaplan games, in this case Flying Shark/Sky Shark. In that game, if an enemy biplane was shot from far enough away, it would indeed crash-land rather than just explode—and destroy any hapless tank, patrol boat, or anti-aircraft gun that happened to be underneath.
Harder Than Hard: Raiden IV has Very Hard difficulty, which in turn is trumped by Ultimate difficulty. That is to say, Harder Than Harder Than Hard.
Product Placement: The Genesis port of the first game adds a really hard level that appears after the credits. Beating it will show a message advertising one of Micronet's (the port developer) game, Heavy Nova.
Recurring Boss: The giant jet bomber that launches missiles that look kind of like smaller planes.
Recurring Boss Template: The first boss battle of the first three games pits you against a duo of ground enemies (gun platforms in the first, spider tanks in II and giant tanks in III) with the weaker one appearing slightly before the other. IV broke the trend by having a single spider tank instead.
Also, there's the missile-carrying bomber in those games' second stages, and the giant aqueous vessel in the third stages (a battlecruiser in I, a submarine in II and III).
Recycled INSPACE: Seibu's ownViper Phase 1 is this series IN SPACE! Its soundtrack is even unlockable in the Playstation port of Raiden DX.
Regional Bonus: The US version of Raiden Project allows the player to turn off the checkpoint behavior in Raiden, which was enforced in the Japanese version. On the downside, it dummies out vertical rotation, requiring the player to use a cheat device if they want to play the game on a vertically-oriented TV.
Sequential Boss: The fifth boss of Raiden II. First you destroy a space shuttle, then fight the fighter it was carrying, and finally face off with the orange jet housed inside it. Also kind of a Climax Boss, considering it's the last level on Earth.
Also the Final Boss, which has you fire at the core of this giant purple obsidian-temple-thing, with more and more crap coming out of the temple (Mooks and bulletfire) as the battle goes on.
Many of the bosses of the later games do this, as well as Turning Red.
Spider Tank: The first Boss(es) of II, also unofficially known as the "Death Walkers". You have to fight two of them (thankfully, not at the same time, unless you're slow in cutting down the first one). One is also the first boss of Raiden IV.
"Gallantry", the st. 1 and 4 music in the first game, has a phrase that sounds a lot like a phrase in "Mystic Green", the st. 4 music from Hellfire (0:25-0:39 in "Gallantry", 0:23-0:37 in "Mystic Green").
Considering the first Raiden game was basically a big Toaplan homage, this makes sense.